Progressive Collapse Resistance of Steel and Composite Frames under Localised Fire Scenarios Near an Internal Column

Local damages to key structural members may originate from different causes, including localised fires or earthquakes, and, as far as the affected area remains small and the damage is contained, the risk is reduced. However, if the structure does not have the capacity to absorb the damage and bridge over the lost components, progressive collapse may be initiated, with serious consequences for the life of the occupants and the costs of losses. Even if some inherent structural properties, like redundancy and ductility, bring a beneficial contribution to the resistance of structures subjected to such scenarios through the activation of alternate load paths, these properties can be affected when working under elevated temperatures, and thus structural integrity can be at risk. This paper investigates the cumulative effects of seismic events and elevated temperature on the progressive collapse resistance of two-way frames with steel and composite steel-concrete floors. Numerical models are calibrated against relevant test data. The results show that, even if fire protection is an effective way in increasing the resistance of structural components under elevated temperatures, the failure may propagate due to the attainment of the bearing capacity of the surrounding elements and connections that are still at ambient temperature. Also, the interaction between concrete slabs and steel beams may provide additional capacity to stop the progressive collapse.